To manufacture a semiconductor device, various kinds of heat treatment apparatuses are used for performing processes including oxidation, diffusion, and Chemical Vapor Deposition (CVD) to a semiconductor wafer to be processed. A general heat treatment apparatus includes a heat treatment furnace which is mainly equipped with a processing vessel for accommodating semiconductor wafers and performing heat treatment, a cylindrical heat insulating member disposed to cover a periphery of the processing vessel, and a heater arranged along an inner peripheral surface of the heat insulating member to heat the wafers accommodated in the processing vessel. The heater includes heating elements arranged along the inner peripheral surface of the cylindrical heat insulating member.
In a heat treatment apparatus for performing a batch process, the heating elements may include a heating member, which is arranged along an inner wall surface of the cylindrical heat insulating member and supported by a supporting member. The heating elements can heat an inside of the furnace to a high temperature of, for example, about 800 to 1000 degrees C. As the heat insulating member, a member formed by sintering a heat insulating material made of, for example, a ceramic fiber, in a cylindrical shape is used. The heat insulating member reduces a heat quantity lost as radiant heat or conductive heat so as to enhance efficiency in heating. As the supporting member, there is used a ceramic member, for example. The ceramic supporting member supports the heating elements at predetermined pitches, while allowing heat expansion and heat shrinkage of the heat elements.
The heat insulating material of the heat treatment furnace is formed of, for example, an inorganic fiber containing silica, alumina or alumina silicate. In addition, various approaches are employed to prevent heat loss from the heat insulating member.
For example, in order to prevent the heat loss from the heat insulating member, a layer thickness of the heat insulating member may be increased. Unfortunately, to achieve an appropriate prevention of the heat loss, a heat insulating member is required to have a substantially increased thickness. Further, a deteriorated temperature increase/decrease performance may occur because of an increase in heat capacity of the heat insulating member. As such, an increased capacity of heater is required.
Further, a heat insulating vacuum member may be employed to the heat insulating member to enhance an insulation property. Unfortunately, such heat insulating vacuum member using a metal vacuum vessel has a poor heat-resistance, and thus, cannot be used under high temperatures. Moreover, a bulk heat insulating vacuum member results in an increase in weight or an increase in the manufacturing cost.